1. Field of the Invention
This invention relates to a metal corrosion inhibitor for use in aqueous solutions, and to antifreeze/coolant compositions containing such a corrosion inhibitor. More particularly, this invention relates to a corrosion inhibitor comprising a combination of monobasic acids or the alkali metal, ammonium, or amine salts of said acids and a hydrocarbyl triazole together with imidazole, and to antifreeze/coolant compositions containing the same.
2. Description of Related Information
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminum, magnesium, and their alloys. The possibility of corrosive attack on such metals is high, due to the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, which may subsequently cause engine overheating and engine component failure due to excess metal temperatures. See generally Fay, R. H., "Antifreezes and Deicing Fluids," in Kirk-Othmer Encyclopedia of Chemical Technology (1978 ed.), vol. 3, pp. 79-95. It would therefore be generally advantageous if the formation of corrosion products within automobile cooling systems could be controlled or eliminated. It is one object of the instant invention to provide a corrosion inhibitor useful in the prevention and control of corrosion in automobile engine cooling systems containing various metals.
The trends towards improved fuel economy for automobiles has led to the increased use of aluminum and in some cases magnesium for engine and cooling system components. However, it has been found that pitting and crevice corrosion are particularly prevalent in aluminum-containing cooling systems. Many conventional corrosion inhibitor additives used in automobile cooling systems do not provide adequate protection against the pitting and crevice corrosion phenomena found with various aluminum and magnesium alloys. It would therefore be particularly advantageous if the pitting and crevice corrosion phenomena found in automobile cooling systems containing aluminum or magnesium alloys could be controlled or eliminated. It is another object of the instant invention to provide a corrosion inhibitor for use in automobile cooling systems which prevents or controls pitting and crevice corrosion of aluminum and magnesium metal surfaces.
Corrosion inhibitors employed in automobile antifreeze/coolant formulations are gradually depleted by use and the build-up of corrosion products in the cooling system. It would thus be advantageous if the build-up of corrosion products within the system and subsequent corrosion inhibitor depletion or degradation could be controlled or eliminated. It is a further object of the instant invention to provide a corrosion inhibitor which is less prone to depletion or degradation than traditional corrosion inhibitors used in antifreeze/coolant formulations.
It is well known that various monobasic acids as well as the salts of such acids are individually effective as corrosion inhibitors when employed in antifreeze/coolant formulations. For example, the use of sodium salts of various monobasic acids as mild steel corrosion inhibitors in aqueous solutions is disclosed in Hersch, P., et al., "An Experimental Survey Of Rust Preventives In Water-II. The Screening Of Organic Inhibitors," Journal of Applied Chemistry, vol. 11 (July, 1961), pp. 254-55. The use of a mixture of sodium sebacate (the sodium salt of sebacic acid) and benzotriazole as a useful corrosion inhibitor in engine coolants is disclosed in G. Butler & A. D. Mercer, "Inhibitor Formulations for Engine Coolants," British Corrosion Journal, vol. 12, no. 3 (1977), pp. 171-74.
Several U.S. and foreign patent references disclose the use of various monobasic acids, or the salts of such acids, as corrosion inhibitors for use in antifreeze/coolant compositions.
U.S. Pat. No. 4,342,596 discloses a corrosion inhibiting composition for metals comprising 5-20 parts of a C.sub.8 -C.sub.20 aliphatic monobasic acid, 0.5-4 parts of a lubricant, 0.5-4.0 parts of an amino alkylalkanolamine, 10-35 parts of an aromatic mono- or polycarboxylic acid, and an amine used to form a water-soluble salt with the aromatic acid.
U.S. Pat. No. 3,573,225 discloses a corrosion inhibitor containing 50-100 parts of a salt of a C.sub.6 -C.sub.18 saturated carboxylic acid, 20-200 parts of an alkali metal benzoate, and 1-50 parts of an alkanolamide selected from the reaction products of ethanolamines and a saturated C.sub.6 -C.sub.18 fatty acid.
British Patent No. 2,122,598 discloses a metal corrosion inhibitor which comprises at least one C.sub.6 -C.sub.10 aliphatic carboxylic acid, at least one C.sub.6 -C.sub.8 polyhydroxycarboxylic acid, and at least one aromatic monocarboxylic acid, in which each of the acids is present as a salt.
U.S. Pat. No. 4,759,864 discloses a corrosion-inhibited antifreeze concentrate formulation containing no phosphate, amine or nitrite consisting essentially of liquid alcohol freezing point depressant, a C.sub.6 -C.sub.12 aliphatic monobasic acid, an alkali metal borate and a hydrocarbyl triazole.
U.S. Pat. No. 4,647,392 discloses a corrosion inhibitor for use in antifreeze systems comprising the combination of a C.sub.5 -C.sub.16 aliphatic monobasic acid, a C.sub.5 -C.sub.16 hydrocarbyl dibasic acid and a hydrocarbyl triazole.
European Patent No. 0,251,480 discloses a corrosion inhibitor for use in antifreeze systems comprising the combination of a C.sub.8 -C.sub.12 aliphatic monobasic acid, an alkylbenzoic acid, and a hydrocarbyl triazole.